For a tiny Australian spider, somersaulting is the secret to taking on ants twice its size.
Ants – armed with mighty jaws and sometimes chemical weapons, are so dangerous to spiders that less than 1 percent of arachnids attempt to hunt insects (Serial number: 8/9/21). High-speed images now reveal that the Australian ant-killing spider (Euryopis umbilicata) can deal with this dangerous prey by jumping and tying its victims with silk.
The hunting maneuver not found in any other spider speciesresearchers report on September 19 in the Proceedings of the National Academy of Sciences.
“This acrobatic behavior is simply fascinating. I personally had never seen this type of hunting,” says Paula Cushing, an evolutionary biologist and curator of invertebrate zoology at the Denver Museum of Nature and Science, who was not involved in the study.
Alfonso Aceves-Aparicio, a behavioral ecologist at the Max Plank Institute for Chemical Ecology in Jena, Germany, came across the cartwheeling spiders while walking home one night. Aceves-Aparicio, a graduate student at Macquarie University in Sydney at the time, was intrigued when he noticed dark dots crossing the pale bark of a eucalyptus tree.
The dots were small spiders that moved among ants. Suddenly, one of the spiders jumped out. “I thought I was trying to get away from an ant,” recalls Aceves-Aparicio. “But then I saw the ant hovering and thought, woah, something is going on here.”
Aceves-Aparicio borrowed a high-speed camera to see what the spiders were doing in greater detail. By slowing down the action, he and his colleagues could see that the spiders were, in fact, hunting ants in a completely unknown way.
Most ant-hunting spiders use webs or sneak up on their prey from behind to minimize risk. But despite being smaller than their prey, the Aceves-Aparicio spiders were up against banded sugar ants (Camponotus consobrinus) Head on. Each spider was positioned so that it could watch the ants as they climbed the tree. As one approached, the spider turned on its prey. Once in the air, the spider hooked a silk thread to the ant.
This single anchor action, performed in the space of milliseconds, determined whether the search would succeed. If the rope got stuck, the spider would swoop around the ant, deftly wrapping more silk around it and ripping it off its feet to drag it down and consume it.
What most caught the attention of Aceves-Aparicio and his colleagues was the effectiveness of the technique. Predators like lions and wolves tend to miss about 50 percent of their intended targets. The success rate of the 60 spider hunts the researchers filmed was a staggering 85 percent.
For Aceves-Aparicio, the discovery shows that extraordinary behaviors can hide in plain sight. “The message here is to be a little curious and pay attention,” she says. “Things are happening everywhere. We just have to be there to find them.”